The present invention relates to fiber optic cables and, more particularly, to tight buffered optical cables.
Conventional tight buffered fiber optic cables form a background of the present invention. For example, U.S. Pat. No. 5,408,564, incorporated by reference herein, discloses a strippable tight buffered optical cable. The cable has an optical waveguide fiber, a protective coating surrounds the outer surface of the fiber, and an interfacial layer surrounds the protective coating. The interfacial layer includes particles of solid lubricant held together with a cross-linked film-forming binder. A buffer layer surrounds the external surface of the interfacial layer. The interfacial layer is designed to provide a very low friction interface between the first protective coating and the buffer layer. The interfacial layer is described as having a thickness of between about 4 to about 15 microns, and is preferably about 5 microns. The layer is formed by the cross-linking of a polymer in which solid particulate ultra high molecular weight polyethylene (UHMWPE) and/or solid polytetrafluoroethylene (PTFE) media have been dispersed. The dispersion has in excess of 90% non-volatiles and the solid particulate lubricant comprises 0.1% to 60% by weight of the dispersion. In terms of function, the solid lubricant, e.g., UHMWPE or PTFE, is designed to provide the desired improved strippability, while the cross-linked binder holds the solid lubricant in place on the first protective coating. The preferred cross-linkable binder is epoxy acrylate polymer.
The foregoing design has certain background characteristics. For example, where the distribution of the solid lubricant in the binder is non-uniform, the strippability forces can vary. In addition, the achievable length of strip can be limited to one foot lengths. Other problems can arise in production, for example, the solid lubricant can cause flaking of the coating. From a manufacturing standpoint, such flaking can result in clogging of the buffer layer extrusion die possibly requiring a shutdown of the manufacturing line. In connection with performance, unintended delaminations between the buffer and fiber can occur. Another issue is microbending caused by the solid lubricant particulates where the interfacial layer surrounds a 50 xcexcm multi-mode fiber. Microbending issues are particularly crucial when the fibers are tight buffered with a thermoplastic or a flame-retardant polyethylene. Such materials can significantly contract during low temperature operations, potentially pushing the solid lubricant particles into microbending contact with the optical fiber.
Additionally, U.S. Pat. No. 5,761,363, incorporated herein by reference, discloses an optical fiber ribbon with an interfacial layer including a non-reactive liquid lubricant material, more particularly, a non-reactive silicone oil that is fugitive and non-compatible with the matrix. No chemical bonding is intended between the matrix and oil or between the matrix and protective coating.
The foregoing design has certain characteristics. For example, the interfacial layer is intended to adhere to the buffer layer rather than the protective coating leaving the protective coating so that the interfacial layer is stripped with the buffer layer. In other words, the fugitive silicone inhibits bonding between the interfacial layer and the protective coatings. Additionally, the silicone oil of 5% to about 19% by weight contributes to manufacturing costs.
One aspect of the present invention provides a tight buffered optical fiber including at least one optical fiber having a protective layer, a release layer and a buffer layer. The protective layer generally surrounds the optical fiber. The release layer generally surrounds the protective layer, at least partially bonding thereto, and includes an acrylate with oligomers, monomers, and a reactive release substance distributed within a matrix. The buffer layer generally surrounds the release layer and may be stripped from the release layer. The reactive release layer preferably includes silicone, more particularly, the release layer may be selected from the group consisting of methyl and phenyl silicones. Moreover, the matrix can be mechanically or chemically bonded to the protective layer so that stripping the buffer layer essentially does not remove the release layer. Additionally, the release layer preferably has a secant modulus of about 20-600 MPa, an elongation to break ratio of preferably less than about 10% and/or a tensile strength of less than about 20 MPa.